Abstract

Quantitative determination of lung density and structure by CT can be of high clinical value, but suitable procedures are needed to ensure reproducibility and objectivity. We present a newly developed, complete protocol for this task which addresses CT measurement as well as image evaluation.

A microcomputer-controlled pocket spirometer is employed to measure vital capacity, to control the level of inspiration during the CT examination and to trigger the scan at a user-selected respiratory level. Evaluation is based on semi-automated algorithms which isolate lung parenchyma by fast contour tracing and define subregions by shrinking and radial and anteroposterior subdividing of the left and the right lung. Global and regional mean density values and histogram parameters are extracted.

Lung density changes by more than a factor of 2 were found in clinical studies as a function of inspirational status. This is a clear indication that tight control of respiratory status is absolutely necessary for reproducible lung density measurements. The evaluation software also improves reproducibility, but above all supports the investigator in his work and provides the possibilities for an extended analysis.